Shock absorber with pressure-controlled damping

ABSTRACT

A damper includes a pressure-sensitive damping control circuit that selectively permits fluid flow from a first chamber to a second chamber. A piston varies a volume of the first chamber. A blow-off piston is movable between a closed position, wherein fluid flow through the control circuit is substantially prevented, and an open position, wherein fluid flow through the control circuit is permitted. The damper also includes a first source of pressure. A fluid pressure created by compression of the damper applies an opening force to the blow-off piston moving the blow-off piston in a direction toward the open position against a resistance force provided by the first source of pressure. The resistance force exceeds the opening force until the pressure created by forces tending to insert the piston rod into the first fluid chamber exceeds the pressure in the first source of pressure by a predetermined amount.

RELATED APPLICATIONS

This application is a continuation of and claims the benefit of U.S.Pat. No. 9,010,504, filed Jun. 20, 2012, entitled “Shock Absorber withPressure-Controlled Damping”, by Dustin F. Janes. U.S. Pat. No.9,010,504 is a continuation of and claims benefit of U.S. Pat. No.8,205,730, filed Mar. 5, 2009, entitled “Shock Absorber withPressure-Controlled Damping”, by Dustin F. Janes. U.S. Pat. No.8,205,730 is a continuation of and claims benefit of U.S. patentapplication Ser. No. 10/888,080, filed Jul. 8, 2004, entitled “ShockAbsorber with Pressure-Controlled Damping”, by Robert C. Fox. U.S.patent application Ser. No. 10/888,080 claims priority to and benefit ofU.S. Provisional Patent Application No. 60/501,903, filed Sep. 10, 2003,entitled “Shock Absorber with Pressure-Controlled Damping”, by Dustin F.Janes. U.S. patent application Ser. No. 10/888,080 also claims priorityto and benefit of U.S. Provisional Patent Application No. 60/485,409,filed Jul. 8, 2003, entitled “Shock Absorber with Pressure-ControlledDamping”, by Robert C. Fox et al. U.S. Provisional Patent ApplicationNo. 60/501,903 and U.S. Provisional Patent Application No. 60/485,409are hereby incorporated by reference in their entirety herein.

INCORPORATION BY REFERENCE

U.S. Pat. No. 8,205,730, filed Mar. 5, 2009; U.S. patent applicationSer. No. 10/888,080, filed Jul. 8, 2004; U.S. Provisional PatentApplication No. 60/501,903, filed Sep. 10, 2003; and U.S. ProvisionalPatent Application No. 60/485,409, filed Jul. 8, 2003, are each herebyincorporated by reference herein in their entireties and made a part ofthe present specification.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to fluid damping control for vehicle suspensions,such as the suspensions of bicycles, which are typically mounted betweenthe bicycle frame (chassis) of the vehicle and a wheel of the vehicle.

Description of the Related Art

Shock absorbers used on motorized and human powered vehicles provide ameans to damp out road vibration, bump energy and substantially increaserider/passenger comfort. The shock absorber component is composed of twoparts. First being the damper, the component that absorbs the bumpenergy and second the supporting spring. It is common in highperformance shock absorbers to have an external reservoir to which theshock fluid can circulate. The fluid that circulates to the reservoir isa result of the shock shaft insertion at the shock absorber. Theinsertion of the shock shaft onto the shock body will occupy a volumethat displaces the oil towards the reservoir. This reservoir can bemounted to the main shock absorber or connected by means of a length ofhigh-pressure hose.

Under certain circumstances, it is advantageous to restrict the flow ofoil (incompressible fluid) into the reservoir. The function of flowrestriction aids in creating compressive direction damping, referred toas compression damping. Compression damping will be created at thereservoir when fluid is displaced from the shock absorber. Thecombination of flow restriction at the main piston within the shockabsorber, for example as a result of flexible washers sealing holes onthe main piston, coupled with compression damping at the reservoir,provides the total compression damping created by the shock absorbersystem. The devices used to create compression damping in the reservoirare of many types. A plate covered by flexible washers is one example ofa device. Other methods employ passages blocked by movable balls orplates forced into position by a spring. A further type of device uses asimple passage that is restricted by a movable protrusion that changesthe clearance between the passage and protrusion.

Another feature known in the art for providing compression damping in aninternally-pressurized shock absorber is an annular cavity containingcompressible fluid formed between the main shock absorber piston and thepiston rod. A second annular piston in sealed engagement with the cavityis driven by pressure forces and reciprocates in the cavity toalternately block the compression damping passageways in the main pistonas the piston approaches the blind end of the shock absorber cylinder,and unblock them as the piston withdraws from the blind end. The annularcavity and the annular piston which reciprocates within it areconfigured coaxially on the main piston and shaft of the shock absorber.See also U.S. Pat. No. 5,190,126.

There is a need in bicycles, motorcycles, and other vehicles whichincorporate fluid suspension shock absorbers for a pressure-controlleddamping circuit in a separate, non-coaxial reservoir. All prior-artmethods, such as those noted above, suffer from various limitations,including an impact on the travel capability within a given shockabsorber length, fixed location and installation requirements, andlimited adjustment range.

SUMMARY OF THE INVENTION

A preferred embodiment involves a pressure sensitive damper including afirst cylinder at least partially defining a first fluid chambercontaining a damping fluid. A damping piston is supported for reciprocalmotion within the first cylinder. A piston rod has a first end, which isconnected to the damping piston, and a second end, which extends througha sealed opening in a seal head fixed to a first end of the firstcylinder. The damper also includes a second cylinder at least partiallydefining a second fluid chamber in selective fluid communication withthe first cylinder and containing a damping fluid. A compression dampingplate is fixed in the second cylinder and includes at least one passagethrough which the damping fluid, displaced by the entrance into thefirst cylinder of successive portions of the piston rod during acompression stroke, flows in a first direction from the first fluidchamber to the second fluid chamber. A first pressure source is incommunication with the second fluid chamber. The damper further includesa valve which generates a resistance force to the fluid flow through theat least one passage in the first direction, wherein the resistanceforce varies according to an amount of force communicated to the valveby the first pressure source. The valve includes a blow-off piston, asupport shaft, a support plate, and an intensifier piston. The blow-offpiston has a first position in engagement with the at least one passageand a second position removed from the at least one passage. The firstpressure source acts on a first end of the intensifier piston. Theblow-off piston, the support shaft, and a second end of the intensifierpiston define a third fluid chamber containing damping fluidtherebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a prior-art embodiment of a suspension unitincluding a monotube shock absorber (“damper”) integrated with anin-line internal floating piston (“ifP”).

FIG. 2 is a cross-sectional view of the prior-art suspension unit ofFIG. 1.

FIG. 3 is a plan view of a prior-art embodiment of a suspension unitincluding a shock absorber (“damper”) having a solid structureconnection to a fluid reservoir.

FIG. 4 is a cross-sectional view of the prior-art suspension unit ofFIG. 3.

FIGS. 5a-5c show three overall views of a preferred embodiment of asuspension unit according to a preferred embodiment of the presentinvention.

FIG. 6 is a cross-sectional view of the suspension unit of FIGS. 5a -5c.

FIGS. 7a-7d include several views of a reservoir assembly of thesuspension unit of FIGS. 5a -5 c.

FIGS. 8a-8c include two cross-sectional views and an end view of thereservoir assembly of FIG. 7.

FIG. 9 is an enlarged view of the intensifier assembly of FIG. 8b ,including designations of the four different internal pressuresoperative in the reservoir.

FIG. 10 is an enlarged view of elements comprising the intensifierassembly of FIG. 9, including designation of the component diameterspertinent to free-body analysis of the operative forces on theintensifier piston and the blow-off piston.

FIG. 11 is a force vs. velocity compression damping graph depicting“Firm” and “Soft” as well as “Knee” damping function.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The prior-art integrated suspension unit 100 of FIGS. 1 and 2 aredescribed first, in order to provide a point of reference for a betterunderstanding of the improvements of a preferred embodiment of thepresent invention, which is described further on.

One example of a typical prior-art shock absorber 100 as shown in FIGS.1 and 2 is manufactured by Fox Racing Shox. It will be understood by oneof ordinary skill in the art, that this specific prior-art embodiment isrepresentative only, and that preferred embodiments of the presentinvention can be applied to other types of shock absorbers, or dampers,as well.

FIGS. 1 and 2 illustrate one example of a prior art shock absorber, orintegrated suspension unit, generally referred to by the referencenumeral 100. The illustrated integrated suspension unit 100 generallyincludes a damper assembly 101 and a biasing member, such as spring 102(shown schematically in FIG. 1). In other arrangements, the biasingmember may comprise an air spring assembly, as will be appreciated byone of ordinary skill in the art.

The major components of the illustrated suspension unit 100 include theseal head 104, shock shaft 105, shock body 106 defining a fluid chamber111, shaft eye 107, body eye 108, gas chamber 109, and main dampingpiston 110.

The ends of the integrated suspension unit 100, the body eye 108, andthe shaft eye 107, are connected to the sprung (e.g., the vehicle body)and un-sprung (e.g., the wheels and wheel support assemblies) portionsof the vehicle (not shown) in a conventional manner. That is, either ofthe ends 107, 108 may be connected to either of the sprung or unsprungportions of the vehicle, depending on the specific application. The coilspring 102 creates a force tending to lengthen the suspension unit 100,while the weight of the vehicle (i.e., the sprung mass) tends to shortenit. As is well known in the art, the net effect of the compression ofthe coil spring 102 under the mass of the vehicle, is known as “sag”.When the integrated suspension unit compresses or sags-in, the shockshaft 105 enters the shock body and decreases the length of the shock(i.e., the distance between the ends 107, 108). When the shock shaft 105enters the shock, a volume of the shock oil contained in fluid chamber111 of the damper assembly is displaced, thus causing the internalfloating piston 103 to move a corresponding distance.

In FIGS. 3 and 4 the integrated suspension unit 200 is comprised of adamper assembly 201 and a biasing member, or coil spring assembly 202(illustrated schematically in FIG. 3), that form the integratedsuspension unit 200. This type of shock is similar to integrated damperassembly 100 with the exception that the internal floating piston 203 isnot positioned coaxially with the shock shaft 205. The piggyback housing214 contains a passage for displaced shock oil 215 to flow through. Thepiggyback housing 214 rigidly secures the reservoir housing 216 to theshock body 206. This type of damper assembly is capable of a reductionin overall length vs. travel in comparison to the integrated damperassembly 100, as a result of the non-coaxially placed high pressure gascharge 209 and internal floating piston 203.

The major components found in integrated suspension unit 200 are similarto components found in the integrated suspension unit 100. For examplethe following components of the illustrated integrated suspension unit200 are typical in a remote reservoir-type suspension unit: seal head204, shock shaft 205, shock body 206 defining a fluid chamber 211, shafteye 207, body eye ring 208, pressurized gas chamber 209, main dampingpiston 210, spring threaded collar 213, reservoir housing 216, piggybackhousing 214, and reservoir end cap 217.

With reference to a preferred embodiment of the integrated suspensionunit 400 illustrated in FIGS. 5 and 6, when the shock compresses, shockoil is displaced to the reservoir assembly 420 through the flexible hose403. The amount of shock oil that is displaced into the reservoirhousing 416 during a given distance of compression travel is generallyequal to the volume of the shock shaft 405 that has entered the mainshock body 406 during the given compression travel. In the process ofthe shock oil being displaced into the reservoir housing 416, preferablyit encounters a structure, or system, that resists the movement, orflow, of the shock oil. Such a structure, or system, provides acompression damping force, tending to resist compression movement of thesuspension unit 400, and may be of any suitable construction, such as arestrictive orifice, shim stacks, check plate(s), for example butwithout limitation, as will be readily appreciated by one of ordinaryskill in the art. The structure, or system, is referred to as thereservoir assembly 420.

Referring back to the prior-art integrated suspension unit 100 of FIGS.1 and 2, the suspension unit 100 did not contain externally-adjustabledamping features. In contrast, the suspension unit 200 of FIGS. 3 and 4includes external adjustment features such as the rebound adjustmentknob 221 and compression adjustment knob 222. The rebound adjustmentknob 221 rotates and has a cone-shaped portion that mates with theadjuster rod 223 end. As the rebound adjuster knob 221 advances (movesin a downward direction in FIG. 4), the complementary interface betweenthe adjuster rod 223 end and cone-shaped portion transfer rotationalmovement of the rebound adjuster knob 221 into linear translation of theadjuster rod 223 (moves to the right in FIG. 4). As the adjuster rodadvances towards the main damping piston assembly 210, it occupies aprogressively larger portion of a passage 224 for shock oil to bypassthe main functional features of the damping piston assembly 210. Ifdesirable, the adjuster rod 223 may completely close off the passage 224to prevent a flow of fluid therethrough. This construction permitsexternal adjustment of rebound damping, as will be understood by thoseskilled in the art.

Although such a rebound damping adjustment feature is not required forapplication of the preferred embodiment, it is illustrated here and isalso included in the illustrated embodiment of the present shockabsorber, as shown in FIGS. 5-10. If this adjustable damping feature isnot included, a somewhat simplified and less costly preferred embodimentof the present invention is made possible.

FIG. 4 illustrates the reservoir compression damping circuit 220 thatfunctions as a “gate” to the shock oil that is displaced from the mainshock body 206 by the volume occupied by the insertion of the shockshaft 205. When the shock oil encounters the reservoir compressiondamping circuit 220, it has two directions that it can flow based on theposition of the compression adjustment knob 222. If the compressionadjustment knob 222 is in a fully counter-clockwise position, thesealing force provided by the compression port seal plate 225 isrelatively light, based on the force that the compression plate spring226 applies to the compression port plate 225 to seal the plate 225against a port 215 a in the piggyback housing 214. Due to the lightsealing force of the compression port seal plate 225, the shock oil willflow through this bypass circuit with relative ease and thereby bypassthe reservoir compression piston 228. The functional dampingcharacteristics that this adjustment position provides are illustratedin FIG. 11 and can be described as “Soft”.

When the compression adjustment knob 222 is in the fully clockwiseposition, the spring load provided by the compression plate spring 226on the compression port plate 225 is at a maximum. The dampingcharacteristic of this compression knob 222 position is illustrated inFIG. 11 and can be described as “Finn”. As a result of the increasedsealing force provide by the compression port plate 225, the shock oilentering the reservoir 216 will take a path of least resistance. In theillustrated embodiment, the path that the shock oil finds leastresistive, in the fully clockwise position of the adjustment knob, isthrough the reservoir compression piston 228 that provides resistance toshock oil flow as a result of flexible metal washers 229 sealing theout-flow face of the reservoir compression piston 228. The flexiblemetal washers 229 are retained on the reservoir compression piston 228by a piston nut 230 and piston bolt 231.

If a position of the compression adjustment knob 222 is between fullyclockwise and fully counter-clockwise, the net compression dampingfunction of both of the shock oil paths described above (through thebypass port 215 or through the reservoir compression piston 228) willinfluence a flow of shock oil into the reservoir housing 216.Furthermore, under certain circumstances, fluid flow may occur throughboth paths even when the compression adjustment knob 222 is in a fullyclockwise or fully anti-clockwise position, as will be apparent to oneof skill in the art. This construction permits external adjustment ofcompression damping, as will be readily appreciated by one of skill inthe art.

The main damping piston 110/210 of the suspension units 100/200, asillustrated in FIGS. 2 and 4, function such that, as the main dampingpiston assembly 110/210 moves through the shock oil 111/211, a dampingforce is produced. Further descriptions of the main damping pistonassembly 110/210 function are not deemed necessary, as one skilled inthe art will understand possible structures and functions of the maindamping piston assembly 110/210, as well as the main damping piston 410of the suspension unit 400 of FIGS. 5-10.

A preferred embodiment of the present shock absorber with pressurecontrolled damping, generally referred to by the reference numeral 400,is described in greater detail with reference to FIGS. 5-10. Componentsor features of the shock absorber 400 not described in detailhereinafter may be assumed to be similar in construction and function tothe same, or similar, components or features of the suspension units100/200 described above. Thus, the description of a preferred embodimentillustrated in FIGS. 5-10 is focused on the illustrated embodiment of apressure controlled damping arrangement.

It is an object of the illustrated embodiment to provide a compressiondamping circuit with a pressure-controlled damping feature that isintegrated with a shock absorber to provide damping control. This typeof circuit provides a method to adjustment of the overall dampingcreated by the shock absorber externally and quickly. Conventionalprior-art designs are limited in adjustment and function. This circuitis particularly applicable to bicycles; however, it may also be readilyadapted for use with other vehicles as well.

In the context of real-world mountain biking, many prior-art methods ofadjusting damping function create a restriction on shock placement orsize, that require reduction in permitted travel and limited dampingadjustment. In contrast, placement of pressure controlled dampingcircuits in a remote location opens up available “dead length” withinthe mounting locations of the main shock body. It is also advantageousto adjust damping function as terrain and trail conditions continuallychange, thus permitting the rider to adjust for the desired ride feel orcurrent situation.

The embodiment illustrated in FIGS. 5-10 achieves this result by placingthe pressure controlled damping circuit in a remote location other thanwithin the axis of the main shock body, thus freeing up space. Incertain preferred embodiments, the pressure controlled damping functionis externally adjustable by pressure adjustment, pressure balanceadjustment, as well as incompressible fluid bypass adjustment, forexample.

In one preferred embodiment, the components within the remote reservoirare arranged and function in the following manner. The oil entering theremote reservoir first encounters a compression damp plate cover, whichis arranged to cover one or more passages in a wall, or compression dampplate. Other passages may exist in the compression damp plate, such aspassages for rebound fluid flow from the reservoir to the main shockbody (referred to herein as “rebound passages”). Preferably, suchpassages include a one-way valve mechanism that substantially preventsfluid flow from the main shock body to the reservoir, but permits fluidflow from the reservoir to the main shock body.

A valve body, or blow-off piston, is configured to selectively cover andsubstantially prevent fluid flow through the passage, thereby creating asealed fluid cavity, or chamber, within the reservoir cylinder. Thiscavity is sealed by force/pressure provided by an incompressible fluidcontained in a separate, intermediate sealed chamber, between theblow-off piston and an intensifier piston. The pressurized fluid withinthe sealed chamber is driven by the intensifier piston, which has a sealat both big and small diameters. The intensifier components are poweredby the internal pressure of the shock that is created by the separatecompressible gas volume, or gas charge, that is isolated from the sealedfluid cavity by an internal floating piston gas separator. The internalpressure of the shock is used to create the sealing force of theblow-off piston. The internal pressure may alternatively be provided byother suitable arrangements, such as a spring-biased floating piston orgas-charged collapsible sleeve, for example.

In order to provide further tune-ability of the blow-off system, aseparate variable volume chamber that contains a compressible gas may belocated between the differing diameters on the intensifier piston. Thispassage or volume has gas introduced by way of an air sleeve surroundingthe reservoir. The pressure of the gas within the variable volumechamber counteracts the pressure that is applied to the end face of theintensifier piston by the internal pressure of the shock itself, which,in the illustrated embodiment, is the pressure within the reservoirchamber produced by the gas charge. With this, the sealing force on theblow-off piston can be reduced to zero, provided that a high enoughcompressible gas pressure is present in the compressible gas volume.

Other components of the pressure controlled damping circuit may includea by-pass circuit, including a by-pass needle controlled by a by-passknob. The external incompressible fluid by-pass needle, when in thefully seated position will not permit fluid to bypass the compressiondamping plate through the bypass port. As the external fluid bypassneedle is backed away from the surface of the compression damping plate,incompressible oil is permitted to flow through the by-pass port.Adjustment of the by-pass knob to permit fluid flow through the bypassport increases the incoming fluid pressure necessary to move theblow-off piston.

Further advantages of the illustrated embodiment include an internalpressure increase based on the position of the shock shaft insertioninto the shock body. The pressure increase in the compressible gasvolume as the shock shaft inserts into the main shock body, in turn,imparts the same amount of pressure increase to the incompressible oilpresent on the other side of the internal floating piston gas separatorwithin the reservoir chamber. This same pressure is imparted on thelargest end face of the intensifier piston, which increases the sealingforce on the blow-off piston, through the intermediate incompressiblefluid chamber. This arrangement provides an increase in sealing force ofthe blow-off piston with the compression damping plate. With this, thecompression damping system of the illustrated shock absorber includesposition sensitive traits that would not otherwise be available in aDeCarbon-type shock absorber, which are strictly velocity sensitive. Inaddition, the preferred embodiment has a wide range of tune-ability, notfound in existing shock systems.

FIGS. 5a-5c are external views of a preferred embodiment of the presentshock absorber. A suspension unit, or shock absorber 400, includes adamper assembly 401, which is similar in external appearance to damperassembly 201, with the exception that the connection between the mainshock body 406 to the reservoir assembly 420 is made with a flexiblehose 403 rather than rigidly mounted with the piggyback housing 214, asis the case with the damper assembly 201 of FIGS. 3 and 4. One skilledin the art will appreciate that the attachment between the “damperassembly” and “reservoir housing” can be made with a rigid mount or hoseand function in a substantially equivalent manner. Further, the flexiblehose 403 offers additional mounting positions of the reservoir assembly420, as compared to the rigid and fixed position offered by thepiggyback housing 214. The illustrated embodiment is shown with aflexible hose, but could also use a rigid mount similar to the piggybackhousing 214.

As with the shock absorbers 100/200 of FIGS. 1 and 3, the embodimentshown in FIG. 5 includes a biasing member, or coil spring 402 (shownschematically in FIG. 5 a), which operates to apply a force tending tolengthen the shock absorber 400. In addition, a spring threaded collar413 functions to increase or decrease a preload on the coil spring 402.

The primary components of the illustrated embodiment shown in FIGS. 5and 6 are similar to the components found in the integrated suspensionunits 100 and 200 of FIGS. 2 and 4, respectively. For example, apreferred embodiment of the present shock absorber includes a flexiblehose 403, a seal head 404, a shock shaft 405, a main shock body 406, ashaft eye 407, a body eye ring 408, a high pressure gas charge 409, amain damping piston 410, a fluid chamber 406 a containing damping fluid,an internal floating piston 412, a spring threaded collar 413, a shockbody end cap 414, and a reservoir assembly 420.

In operation, when the shock compresses, damping fluid is displaced fromthe compression chamber 406 a of the main shock body 406 to thereservoir assembly 420 through the flexible hose 403. The amount ofdamping fluid displaced into the reservoir assembly 420 during a givencompression travel of the shock absorber 400 is equal to the volume ofthe shock shaft 405 that has entered the main shock body 406 during thecompression travel (i.e., a shaft displacement arrangement). In theprocess of the damping fluid being displaced into the reservoir assembly420, it encounters a flow restriction that resists the movement, orflow, of the damping fluid into the reservoir, thus producing a dampingforce tending to resist compression motion of the shock absorber 400, aswill be described more fully further on. In addition, compressiondamping forces may also be produced by the main damping piston 410. Withreference to FIGS. 8a and 8b , a preferred embodiment of the reservoirassembly 420 is described. As described above, preferably, the reservoirassembly 420 enables an increase in the available shock absorber travelfor a given overall length of the shock absorber 400.

The reservoir housing 416 preferably is a hollow, cylindrical tube,which is closed at a first end by a first end cap 417 and closed at asecond end by a second end cap 419. A floating piston 412 separates theinterior of the reservoir housing 416 into a sealed compressible fluidchamber, or gas chamber 409, and a sealed incompressible fluid chamber,or damping fluid chamber 448. An inlet port 417 permits damping fluid toenter the reservoir housing 416 from the damper assembly 401. An inletport 419 a permits compressible gas, such as nitrogen for example, to beintroduced into the gas chamber 409.

The compression damp plate 431 forms an internal wall within the dampingchamber 448 and includes at least one compression flow passage 431 apassing axially therethrough. In addition, preferably, the compressiondamp plate 431 includes one or more rebound flow passages 431 b passingaxially therethrough. A one-way valve arrangement permits rebound fluidflow to flow through the rebound flow passages, but substantiallyprevents compression fluid flow from passing through the rebound flowpassages. In the illustrated arrangement, the one-way valve mechanismincludes a check plate, or cover plate 432, which is biased into contactwith the compression damp plate 431 by a biasing member, such as spring443, to cover the rebound flow passages. Rebound fluid flow through therebound flow passages is permitted against the biasing force of thespring 443, which preferably is relatively light. Shock absorber rebounddamping forces are generated at the main piston 410, as will beappreciated by one of skill in the art. Passage(s) 431 a are provided inthe compression damp plate 431 to permit compression fluid flow, and areselectively closed by a valve body, or blow-off piston 429, as isdescribed in greater detail below.

The blow-off piston 429 closes the compression flow passage(s) 431 aduring rebound motion of the shock absorber 400. Thus, rebound fluidflow from the reservoir cylinder 416 to the main shock body 406preferably occurs through the rebound flow passages as described above.

In the illustrated embodiment, the reservoir assembly 420 also includesa bypass circuit 415 a. The illustrated bypass circuit 415 a includes atapered needle 415 c and an orifice 415 b, wherein orifice 415 b passesaxially through the compression damp plate 431. A tapered end of aneedle 415 c is positioned coaxially with the orifice 415 b and isaxially adjustable to occupy a greater, or lesser, portion of thecross-sectional area of the orifice 415 b. An axial position of theneedle 415 c is adjustable by an adjustment knob 415 in threadedengagement with the end cap 417 and which supports, or is integral with,the needle 415 c. Thus, fluid is permitted to flow through the orifice415 b in both compression and rebound directions. In a compressiondirection, the fluid may bypass the compression passage(s) 431 a, flowthrough which is controlled by the blow-off piston 429, as is describedin greater detail below. Preferably, the needle 415 c is adjustable to aposition to completely close the orifice 415 b and effectively eliminatethe bypass circuit 415 a. In other arrangements, the bypass circuit 415c may be omitted entirely, as will be appreciated by one of skill in theart.

Preferably, a support assembly extends in an axial direction from theend cap 417 into the damping chamber 448 to support additionalcomponents of the reservoir assembly 420, including the blow-off piston429. The support assembly preferably includes a support shaft 430 and asupport plate 438 extending from the end cap 417 in that order. Thesupport plate 438 is secured to an end of the support shaft 430 oppositethe end cap 417. A seal 437 creates a substantially fluid-tight sealbetween an external surface of the support shaft 430 and an internalsurface of the support plate 438.

The support shaft 430 includes a small diameter end, nearest the end cap417, and a large diameter end. The large diameter end defines a centralcavity 430 a, which opens at an end surface of the large diameter endopposite the end cap 417. An orifice 430 b extends in a radial directionthrough the support shaft 430 from the cavity 430 a. The support plate438 includes a passage 438 c extending axially therethrough. The passage438 c is aligned with the cavity 430 of the support shaft 430 and,preferably, the cavity 430 has a smaller diameter than the passage 438c. An outer peripheral surface of the support plate 438 supports seals436, which create a fluid tight seal with the internal surface of thereservoir housing 416. In addition, the support plate 438 includes oneor more axial ports 438 b, which permit damping fluid flow substantiallyunrestricted therethrough.

An intensifier piston 440 is supported for axial movement within thecavity 430 a and passage 438 c of the support plate 438. The smalldiameter end of the intensifier piston 440 is supported by the cavity430 a and the large diameter end of the intensifier piston 440 issupported by the passage 438 c. Seals 441, 442 create an at leastsubstantially fluid tight seal between the intensifier piston 440 andthe cavity 430 a and passage 438 c, respectively. A retaining ring 439limits movement of the intensifier piston 440 in a direction away fromthe end cap 417.

The blow-off piston 429 is supported for axial movement on the supportshaft 430 and includes an internal recess 429 a, which together with anexternal surface of the support shaft 430 defines an interior chamber.Seals 427, 428 create a fluid tight seal between the external surface ofthe support shaft 430 and the blow-off piston 429. The internal recess429 a is sized and shaped such that the internal chamber of the blow-offpiston 429 communicates with the cavity 430 a of the support shaftthrough the orifice 430 b, preferably in all axial positions of theblow-off piston 429. Thus, the chamber, defined by the internal recess429 a, and the cavity 430 a cooperate to form an intermediateincompressible fluid chamber 433. Damping fluid within the intermediatechamber 433 is pressurized by a small diameter end of the intensifierpiston 440 and applies a force tending to move the blow-off piston 429against the damp plate 431 to close the passage(s) 431 a. The forceapplied by the pressurized fluid within the intermediate chamber 433 tothe surfaces of the blow-off piston 429 within the recess closest to theend cap 417 tends to move the blow-off piston 429 toward a positionclosing the passage(s) 431 a.

With reference to FIG. 8a , the blow-off piston 429 includes a closablefill port 429 b. The fill port 429 b permits the fluid chamber 433 to befilled with incompressible damping fluid during assembly of thereservoir assembly 420.

With continued reference to FIG. 8a , preferably the reservoir assembly420 includes an adjustment mechanism that permits adjustment of thepressurization force applied to the fluid within the intermediatechamber 433 by the intensifier piston 440. More preferably, theadjustment mechanism applies a force to the intensifier piston 440tending to counteract motion of the intensifier piston 440 into thecavity 430 a of the support shaft 430. In the illustrated arrangement, acompressible gas chamber 445 is defined by the support plate 438. Anintermediate section of the intensifier piston 440, between the seals441, 442, passes through the gas chamber 445. A pressurized gas withinthe gas chamber 445 acts on the transition surface between the small andlarge diameter ends of the intensifier piston 440 to apply a forcetending to move the intensifier piston 440 out of the cavity 430 a.

Preferably, a gas pressure level within the gas chamber 445 isadjustable. In the illustrated arrangement, a sleeve 421 surrounds thereservoir housing 416 adjacent the gas chamber 445 and includes an inletvalve 418, which permits gas, such as nitrogen, to be introduced intothe gas chamber 445, thereby adjusting a pressure level within thechamber 445. One or more passages 446 may extend through the reservoirhousing 416 to permit the gas chamber 445 to communicate with a spacebetween the sleeve 421 and an outer surface of the housing 416.

In addition, preferably, a volume of the gas chamber 409 defined by thefloating piston 412 and the reservoir housing 416 is adjustable. In theillustrated arrangement, a sleeve 449 surrounds an end of the reservoirhousing 416 adjacent the end cap 419. An inner surface of the sleeve 449has a larger diameter than an outer surface of the reservoir housing 416to define a space 449 a therebetween. An end of the sleeve 449 closestto the end cap 419 is sealed with an external surface of the reservoirhousing 416 by a seal 450.

A movable seal 451 contacts an inner surface of the sleeve 449 and anouter surface of the reservoir housing 416 to seal the space 449 a at anend of the sleeve 449 furthest from the end cap 419. The movable seal451 is movable relative to the sleeve 449 to vary a volume of the space449. The position of the movable seal 451 is controlled by a collar 423,which engages the movable seal 451, and a nut 422. The nut 422 isthreadably engaged with the housing 416 such that rotation of the nut422 moves the collar 423 axially relative to the housing 416 to move themovable seal 451 and vary the volume of the space 449 a. The space 449communicates with the gas chamber 409 via one or more ports 449 bextending through the reservoir housing 416. Thus, varying the volume ofthe space 449 varies the volume of the collective volume of the gaschamber 409 and space 449, thus varying the pressure therewithin.

In operation, as the damping fluid contained within the shock body 406is displaced by the insertion of the shock shaft 405, damping fluid isconveyed to the reservoir assembly 420 by the attached flexible hose403. The entering damping fluid passes into the reservoir end cap 417through the port 417. The damping fluid within the sealed incompressiblefluid chamber 433 is pressurized by the intensifier piston 440 that hasa seal at both big and small diameters. Due to the differing diameterscontained on the outside of the intensifier support shaft 430, dampingfluid driven by the intensifier piston 440 is forced into the space 429a contained between sealed surfaces of the intensifier support shaft 430and the blow-off piston 429. The ratio of differing diameters on theintensifier piston 440 as compared to the ratio of differing diametersbetween the intensifier shaft 430 and blow-off piston 429 create amagnification of force/pressure.

The reservoir assembly 420 is powered by the high-pressure gas chargewithin the gas chamber 409 that is isolated from the damping fluid bythe internal floating piston 412. Given a static condition, thehigh-pressure gas charge 409, located between the internal floatingpiston 412 and the reservoir end cap 419, places the same pressure onthe damping fluid. As a result of the high pressure gas charge in gaschamber 409, the combined system of components referred to as “theintensifier”, preferably including the blow-off piston 429, intensifierpiston 440, support shaft 430, compression damp plate 431, and supportplate 438 cause the end face of the compression damp plate 431 to sealagainst the blow-off piston 429. This provides a compression dampingfunction that can be characterized as a “Build pressure and dump” typeof action. This can be described as a “knee” or “nose” as one skilled inthe art would understand. This can be graphically depicted as shown inFIG. 11. This type of damping function is desirable for certainapplications as it provides, for example when utilized in a bicycleshock absorber, an increase in pedaling efficiency, in that each downstroke of the pedals does not result in as much compression movement ofthe suspension as would normally occur with a prior art suspensionassembly.

In order to provide further external adjustability of the reservoirassembly 420, a separate chamber 445 that contains a compressible gas isprovided, as described above. The pressure/volume of compressible gascontained within this region acts upon the area on the intensifierpiston 440 between the two sealing means 440 and 442. As a result of thediffering diameters that exist between the sealing means, a variablepressure/volume is present. This variable pressure/volume permits theadjustment of contained compressible gas to counteract thepressure/force that is applied to the end face of the intensifier piston440 that is on the damping fluid side of the system, next to theinternal floating piston 412. With this in mind, the sealing force onthe blow-off piston 429 can be reduced along with the resultant blow-offforce. Although this feature is not required, it is illustrated and itis also included in the preferred embodiment of the present invention asshown in FIGS. 5-10. If this adjustable damping feature is not included,a somewhat simplified and less costly preferred embodiment is possible.

Further advantages of the illustrated embodiment include a compressiondamping force influenced by the position of the shock shaft 405insertion into the main shock body 406 and how this relates to thepressure increase in the high pressure gas charge 409. The pressureincrease in this region will impart the same amount of pressure increaseto the “incompressible” damping fluid present on the other side of theinternal floating piston 412. This same pressure/force is imparted onthe largest end face of the intensifier piston 440, that in turnincreases the sealing force on the blow-off piston 429 the deeper theshock shaft 405 is inserted into the main shock body 406. This willprovide an increase in sealing force; hence more compression damping.This is highly advantageous to provide position-sensitive compressiondamping forces. With this arrangement, tune-ability of the compressionsystem is obtained with position sensitive traits that would nototherwise be available in a conventional DeCarbon-type shock absorber.In addition, the preferred embodiment has a wide range of tune ability,not found in other shock systems.

The following example mathematically demonstrates the function andrelation of the preferred control system. With reference to FIG. 9,showing pressures, and FIG. 10 showing pertinent feature diameters, afree-body analysis of the blow-off piston 429 gives:

Referring to the feature diameters per FIG. 10, it is convenient todefine the relevant areas of the blow-off piston 429 and the intensifierpiston 440 acted upon by the various internal pressures as follows:A1=[π/4]*[D1² −D5²] {ref: 429—acted upon by P1; to the RIGHT}A2=[π/4]*[D1² −D2²] {ref: 429—acted upon by P2; to the LEFT}A3=[π/4]*[D3²] {ref: 440—acted upon by P2; to the LEFT}A4=[π/4]*[D4²] {ref: 440—acted upon by P4; to the RIGHT}A5=[π/4]*[D2² −D5²]{ref:429—acted upon by P4; to the LEFT}A6=[π/4]*[D3² −D4²] {ref: 440—acted upon by P3; to the RIGHT}

Still referring to FIGS. 9 and 10, the forces acting on blow-off piston429 are:Forces to the RIGHT=[P1]*[A1]Forces to the LEFT=[P2]*[A2]+[P4]*[A5]

Based on free-body analysis, when blow-off piston 429 opens (moves tothe right), these forces are equal, and the following relationshipholds:[P1]*[A1]−[P2]*[A2]+[P4]*[A5]

Re-arranging gives the following expression for pressure PI as afunction of feature areas (diameters), reservoir pressure P2, andintensifier pressure P4:PI=[P2]*[A2/A1]+[P4]*[A5/A1]  {Equation #1}

Next, the forces acting on intensifier piston 440 are:Forces to the RIGHT=[P4]*[A4]+[P3]*[A6]Forces to the LEFT=[P2]*[A3]

For equilibrium conditions (i.e., under normal operation conditionswhere the intensifier piston 440 is freely-floating, neither topped-outnor bottomed-out in its travel), these forces are equal:[P4]*[A4]+[P3]*[A6]=[P2]*[A3]Re-arranging gives:P4=[P2]*[A3/A4]−[P3]*[A6/A4]  {Equation #2}

By substituting the right side of Equation #2 for P4 in Equation #1above, an expression for pressure P1 is determined as a function ofspecific feature areas (diameters), the pre-set reservoir pressure P2,and the adjustable pressure P3:P1=[P2]*[A2/A1]+{[P2]*[A3/A4]−[P3]*[A6/A4]}*[A5/A1]  {Equation #3}

The compression damping force thus produced by the pressure-sensitivereservoir assembly 420 of the present invention is equal to the abovevalue of P1 minus reservoir pressure P2, times the cross-sectional areaof the shock absorber shaft 405. (Note that reservoir pressure P2 actingon the area of the shock absorber shaft is subtracted here; it creates a“nose force” tending to extend the shock absorber at all times, but, asis known in the art, this is considered a static force, not a dampingforce.) Of course, as contemplated by the present invention, there willgenerally be additional compression damping forces produced by fluidflow restrictions at the main shock absorber damping piston 410.

Following is a Numeric Example

P2=100 psi

P3=0 psi

DI=0.625″

D2=0.400″

D3=0.375″

D4=0.250″

D5=0.312″

Substituting these values into the above equations for areas gives:

A1=0.230 in²

A2=0.181 in²

A3=0.110 in²

A4=0.049 in²

A5=0.049 in²

A6=0.061 in²

Inserting these values, as well as P2=100 psi and P3=0 psi into Equation#3 above gives:

P1=127 psi

As is apparent, if P3 is changed, the result of the equilibrium equationwill be different. This demonstrates to the ability to tune the pressureblow-off threshold by changing the volume of the gas chamber 409, whichchanges the pressure therein.

Further advantages of the illustrated embodiment are provided by thealternate path for damping fluid provided by the compression by-passbleed circuit 415 a. When the compression by-pass bleed circuit 415 a isin the fully “in” or full clock-wise position, no alternate path fordamping fluid exists and all damping fluid being displaced from the mainshock body 406 must move through the passage 431 a found in thecompression damp plate 431 by moving the blow-off piston 429. As thecompression bypass bleed screw 415 is turned in a counter-clockwisedirection, it presents an alternative path for the damping fluid to passto the opposite side of the compression damp plate 431. The function ofthis “alternative path” is such that it decreases the low shaft velocitycompression damping that is created by the reservoir assembly 420. As afurther consequence of the size/diameter of the “alternative path,” theoverall decrease in compression damping is such that the “alternativepath” can't pass the entire volume of damping fluid that is flowing tothe compression damp plate 431. If this adjustable damping feature isnot included, a somewhat simplified and less costly preferred embodimentis possible.

Although this invention has been disclosed in the context of certainpreferred embodiments and examples, it will be understood by thoseskilled in the art that the present invention extends beyond thespecifically disclosed embodiments to other alternative embodimentsand/or uses of the invention and obvious modifications and equivalentsthereof. In addition, while a number of variations of the invention havebeen shown and described in detail, other modifications, which arewithin the scope of this invention, will be readily apparent to those ofskill in the art based upon this disclosure. It is also contemplatedthat various combinations or subcombinations of the specific featuresand aspects of the embodiments may be made and still fall within thescope of the invention. Accordingly, it should be understood thatvarious features and aspects of the disclosed embodiments can be combinewith or substituted for one another in order to form varying modes ofthe disclosed invention. Thus, it is intended that the scope of thepresent invention herein disclosed should not be limited by theparticular disclosed embodiments described above.

What we claim is:
 1. A pressure-sensitive damper, comprising: a firstcylinder at least partially defining a first fluid chamber, said firstfluid chamber containing a damping fluid; a damping piston forreciprocal motion within said first cylinder; a piston rod comprising: afirst end connected to said damping piston; and a second end extendingthrough an end of said first cylinder; a second cylinder at leastpartially defining a second fluid chamber in fluid communication withsaid first cylinder; a compression damping plate fixed in said secondcylinder; at least one passage in said compression damping plate throughwhich said damping fluid, which is displaced by a movement of saidpiston rod, flows in a first direction from said first fluid chamber tosaid second fluid chamber to achieve a first fluid flow; a firstpressure source in communication with said second fluid chamber; a valvefor generating a resistance force to said first fluid flow, wherein saidresistance force varies according to an amount of force communicated tosaid valve by said first pressure source, wherein said valve comprises:a blow-off piston having a first position in engagement with said atleast one passage and a second position removed from said at least onepassage; an intensifier piston comprising: a first end; and a secondend, wherein said first pressure source acts on said first end of saidintensifier piston and generates an intensified pressure at said secondend of said intensifier piston, wherein said intensified pressure iscommunicated to said blow-off piston to create a first force urging saidblow-off piston toward said first position; and a second pressure sourceacting on said intensifier piston, said second pressure source adaptedto generate a second force tending to counteract an amount of said firstforce communicated to said valve by said first pressure source.
 2. Thepressure-sensitive damper of claim 1, further comprising: a by-passcircuit adapted to permit a flow of said damping fluid in said firstdirection through said compression damping plate without passing throughsaid at least one passage.
 3. The pressure-sensitive damper of claim 1,wherein a pressure level of said first pressure source is adjustable. 4.The pressure-sensitive damper of claim 1, wherein a pressure level ofsaid second pressure source is adjustable.
 5. The pressure-sensitivedamper of claim 1, wherein said first pressure source comprises: apressurized, compressible chamber containing compressible fluid.
 6. Thepressure-sensitive damper of claim 5, wherein said first pressure sourceadditionally comprises: an annular chamber with externally-adjustablevolume.
 7. The pressure-sensitive damper of claim 1, wherein saidblow-off piston moves in an axial direction between said first positionand said second position.
 8. A pressure-sensitive damper, comprising: afirst cylinder at least partially defining a first fluid chamber, saidfirst fluid chamber containing a damping fluid; a damping piston forreciprocal motion within said first cylinder; a piston rod comprising: afirst end connected to said damping piston; and a second end extendingthrough an end of said first cylinder; a second cylinder at leastpartially defining a second fluid chamber in fluid communication withsaid first cylinder; a compression damping plate fixed in said secondcylinder; at least one passage in said compression damping plate throughwhich said damping fluid, which is displaced by a movement of saidpiston rod, flows in a first direction from said first fluid chamber tosaid second fluid chamber to achieve a first fluid flow; a firstpressure source in communication with said second fluid chamber; a valvefor generating a resistance force to said first fluid flow, wherein saidresistance force varies according to an amount of force communicated tosaid valve by said first pressure source, wherein said valve comprises:a blow-off piston having a first position in engagement with said atleast one passage and a second position removed from said at least onepassage; an intensifier piston comprising: a first end; and a secondend, wherein said first pressure source acts on said first end of saidintensifier piston and generates an intensified pressure at said secondend of said intensifier piston, wherein said intensified pressure iscommunicated to said blow-off piston to create a first force urging saidblow-off piston toward said first position; a second pressure sourceacting on said intensifier piston, said second pressure source adaptedto generate a second force tending to counteract an amount of said firstforce communicated to said valve by said first pressure source; and aby-pass circuit adapted to permit a flow of said damping fluid in saidfirst direction through said compression damping plate without passingthrough said at least one passage.
 9. The pressure-sensitive damper ofclaim 8, wherein a pressure level of said first pressure source isadjustable.
 10. The pressure-sensitive damper of claim 8, wherein apressure level of said second pressure source is adjustable.
 11. Thepressure-sensitive damper of claim 8, wherein said first pressure sourcecomprises: a pressurized, compressible chamber containing compressiblefluid.
 12. The pressure-sensitive damper of claim 11, wherein said firstpressure source additionally comprises: an annular chamber withexternally-adjustable volume.
 13. The pressure-sensitive damper of claim8, wherein said blow-off piston moves in an axial direction between saidfirst position and said second position.